Connectors for railcars are usually pivotally attached to each end of a car center sill. A convex end of a male connector part normally rests against a follower block held within a female sill pocket casting that is mounted within the car sill to withstand longitudinal forces tending to thrust the connector into the sill (compressive or buff loading). The connector is held from being pulled from the sill (draft loading) by a pin or drawbar or by a collar that is spaced from the follower block. For consistent orientation in the following text, the terms "forward" will refer to the longitudinal direction into the female pocket, the term "rear" (or rearward) will refer to the opposite direction, and the term "lateral" will refer to a direction transverse to longitudinal .
Several types of connectors are available to extend between successive railcars such as couplers, drawbars and articulated connectors. In coupler and drawbar connections, there are female sill pockets at each railcar platform end and a male connector member is received in each. Thus, relative movement between successive platforms is divided between the two connector ends. That is, if the successive platforms are angled 10 degrees each of the two male connectors will move only 5 degrees. However, in articulated connectors, there is a single pivotal connection between a single set of male and female members that are rigidly attached respectively to the adjacent ends of successive car platforms. Thus, when articulated platforms angle 10 degrees, the single male connector must move 10 degrees in the female pocket.
In newly assembled connectors, the clearances between the aforementioned parts are minimal, and there is virtually no slack or movement of the parts longitudinal of the car when forces on the connectors are reversed, as occurs each time the car is accelerated or decelerated. However, usage induces wear on various parts, and gradually, spaces will be created. Such spaces are known as slack. Slack is undesirable as it causes repetition and magnification of impact forces when a train of cars is accelerated and decelerated. Yet a degree of slack in each pivotable connection is needed for the purposes of assembling and disassembling the parts, which must be done from time to time.
Ordinarily in freight car construction, slack is compensated and taken up by locating a wedge-shaped shim between two of the connector parts, usually between the follower block and a closed end of a sill pocket as shown in prior U.S. Pat. Nos. 3,716,146, 4,456,133 and 4,549,666. As will be seen in the prior art, the wedge usually inserts downwardly by gravity although it can be spring loaded in other directions. In articulated connectors a wedge is placed between the follower block and an end wall of the female member as shown in prior U.S. Pat. Nos. 4,258,628, 4,336,758 and 4,593,829. In operation, the wedge becomes further inserted to maintain compression between the parts as wear enlarges the spaces.
It has now been found that when the aforementioned connector parts are first assembled and operated, the wedge will assume a position that will cause binding and excessive wear between the parts during early service life. Unfortunately, this leads to accelerated and uneven wear and overall will shorten the service life of the parts, particularly the wedge. The problem is in part caused by the connector, follower and wedge components being unmachined cast steel (preferably manganese steel). That is the components, have mating surfaces that are cast to include congruent curved and angled surfaces, and the "as cast" tolerances do not result in ideal mating surfaces due to varying radii, angles, and imperfect features of cast surfaces. The components have not been machined for reasons of economy. Heretofore, it has been assumed that the mating surfaces would wear into appropriate proper fit during a break-in portion of early service life. However, it is now known that a, heretofore unrecognized, degree of premature wear has occurred. Furthermore, the premature wear has been an even larger problem in articulated connectors where relatively greater angling occurs in the connector member.